There are various methods of completion and production in relation to an oil or gas well. Typically, an oil or gas well is completed by cementing casing strings in place along substantially the entire depth of the well. Once the well is completed, production can commence. To facilitate the production of hydrocarbons or other fluids from the well, production tubing is typically installed within the cased wellbore. Production tubing is set in a portion of the well generally concentric with the casing. The production tubing allows communication of the producing zone of the well with the surface.
After the casing and production tubing are installed in the well, there is often the need for various procedures to be performed on the well, such as perforating the well, well logging operations, and the like, to bring the well into productive status. These procedures are performed with tools that are typically attached to what is known as a wireline. The wireline is essentially a metallic, braided cable with a plurality of electrical conductors contained therein, or is often just a metallic braided cable. The various tools that are to be used for a given operation are lowered into the well on the end of the wireline and then activated and/or monitored at the surface by an operator. When operations with the tools are complete, the wireline and attached tools are pulled to the surface and removed from the well so that production can commence or resume, or so that further operations can be conducted in the well.
Occasionally, downhole tools become stuck in the well during the retrieval process. Downhole tools can become stuck in a well for various reasons, such as encountering a restriction that has formed in the inner diameter of the wellbore. Additionally, downhole tools sometimes become bridged over, or the line on which the tools are run becomes key-seated in the walls of the well bore, thereby hindering or preventing removal of the tools from the well. Often, these downhole tools are very expensive pieces of electronic instrumentation and/or have radioactive sources contained therein, and, thus, they must be retrieved from the well. Moreover, these tools often present a hindrance to further operations in or production from the well and therefore they must be retrieved from the well. The procedure of retrieving a stuck tool is typically known as “fishing.”
For situations in which the stuck tool is still attached to an intact wireline, either a cable-guided fishing method (also known as the “cut and strip” method) or a side-door overshot method is typically used to retrieve the tool. The cable-guided fishing method is typically used for deep, open-hole situations or when a radioactive instrument is stuck in the hole. For these situations, the cable-guided fishing method is a safe method that offers a high probability of success. In particular, the cable-guided fishing method allows retrieval of the stuck tool while the tool remains attached to the cable, thereby minimizing or removing the possibility that the tool will fall down the well during the fishing operation, and allowing for the well bore to be cleared with a minimum of downtime. Further, in some instances, through the use of the cable-guided fishing method, the expensive multi-conductor cable can be salvaged.
The cable-guided fishing method is performed with a special set of tools, hereinafter referred to as the “fishing assembly.” The fishing assembly typically comprises a cable hanger with a T-bar, a spearhead rope socket, a rope socket, one or more sinker bars, a spearhead overshot, and a “C” plate. To use the fishing assembly, the individual components of the assembly are assembled together in a series of steps. Specifically, a typical procedure for assembling the individual components of the fishing assembly is as follows (refer to FIG. 1 for a depiction of the individual components of the fishing assembly in their relative positions during and after assembly):                (1) a light pulling force is exerted on the wireline to remove any slack;        (2) a cable hanger (A) is attached to the wireline at the well head;        (3) the wireline is lowered until the cable hanger (A) rests on the well head or rotary table;        (4) the wireline is cut a short distance above the cable hanger (A);        (5) a spear head rope socket (B) is then “made up” to the end of the lower half of the severed wireline above the cable hanger (A);        (6) a rope socket (C) (“the upper rope socket”) is made up to the end of the upper severed half of the wireline;        (7) one or more sinker bars (D) are connected to the upper rope socket (C);        (8) a spear head overshot (E) is connected to the lowermost sinker bar (D);        (9) the spear head overshot (E) is then engaged with the spear head rope socket (B), and a “test strain” is exerted on the assembly by “pulling” on the wireline to ensure that the components are properly connected;        (10) with the spear head overshot (E) engaged with the spear head rope socket (B), the wireline is then “pulled” to exert a force sufficient to raise the cable hanger (A) so that it can be removed from the assembly;        (11) after removing the cable hanger (A) from the assembly, a “C” plate (F) is placed under a specially-shaped section of the spear head rope socket (B);        (12) with the specially-shaped section of the spear head rope socket (B) resting on the “C” plate (F), the entire assembly can be lowered such that the “C” plate (F) rests on the well head or rotary table.After assembling the individual components of the fishing assembly in this (or a similar) manner, the assembly can be used to “fish” the stuck tool out of the well.        
In operation, the fishing assembly fishes the stuck tool out of the well in a series of steps. Specifically, the following steps are typical of the operation of the fishing assembly (refer to FIG. 2 for a depiction of the individual components of the fishing assembly in their relative positions during operation):                (1) the spear head overshot (E) is disconnected from the spear head rope socket (B) and raised up to the derrick man;        (2) the derrick man will then thread the spear head overshot (E) and sinker bar (D) through the first stand of pipe (G) to be run into the well as part of the fishing operation;        (3) the driller will then pick up the first stand of pipe (G) and suspend it over the well head;        (4) the spear head overshot (E) should then be connected to the spear head rope socket (B), a light strain taken on the cable, and the “C” Plate (F in FIG. 1) removed;        (5) the first stand of pipe (G) is then run in the well bore and the slips (H) are set;        (6) the “C” Plate is then replaced, and the assembly is allowed to rest on the tool joint;        (7) the spear head overshot (E) is then disconnected and raised back up to the derrick man;        (8) the derrick man threads the spear head overshot (E) and sinker bar (D) through the next stand of pipe (I), which in turn is picked up by the driller and suspended over the well head through use of the rig's elevator (J);        (9) the spear head overshot (E) is connected to the spear head rope socket (B), the “C” Plate is removed, and the second stand of pipe (I) is stabbed into and made up to the first stand of pipe (G) and run into the well bore;        (10) the “C” Plate is replaced, the spear head overshot (E) is again disconnected and raised up to the derrick man, and the procedure is repeated until enough pipe has been run into the well to contact and free the stuck tool;        (11) after the fish has been contacted and pulled free, the cable hanger (A in FIG. 1) is again placed on the cable, the rope sockets (B, C) are removed from the cable, and the cable tied together with a square knot;        (12) the elevator (J) is then latched around the “T” bar on the cable hanger, and a strain sufficient to pull the cable out of the tool is taken;        (13) the cable hanger is then removed, and the free cable is spooled on to a service truck reel;        (14) the fishing string along with the fish may then be pulled from the hole in the conventional manner.        
While the fishing assembly and method of use described in the preceding paragraphs has proven to be quite successful, difficulties have arisen with some of the prior art components of the fishing assembly. For example, prior art spear head overshots typically require a three-prong “wedge” release tool to disengage the spear head from the spear head overshot. This three-prong “wedge” release tool requires rig floor personnel to effectively wrap the release tool around the spear head overshot, thereby putting the rig floor personnel in extremely close proximity to the fishing assembly and associated tubing. As one of ordinary skill in the art will recognize, close proximity to the fishing assembly and tubing presents a significant safety concern. Accordingly, the following improved spear head overshot eliminates the need for this close proximity and provides a safer and more efficient means to disengage the spear head from the spear head overshot.